This invention relates to an aerosol antiperspirant composition with high efficacy and improved stability.
It is known that the antiperspirant efficacy of aluminum chlorhydrate salts can be significantly improved by heat ageing aluminum chlorhydrate solutions under certain conditions. In this regard, see for example, GB 2,048,229 and U.S. Pat. No. 4,359,456, which are incorporated herein by reference. Thus, it is generally known that heating a solution of aluminum chlorhydrate of relatively low concentration (generally under 20% and preferably about 10%) at a temperature above 50.degree. C. (preferably about 80.degree. C.) for a significant period of time (typically 16 hours or more) will shift the form of the aluminum species present in the composition to a much more efficacious form. This highly efficacious form is unstable in solution and must be rapidly dried after conversion in order to obtain a high efficacy aluminum chlorhydrate salt. This salt, when reconstituted as a 10% aqueous solution and promptly subjected to size exclusion chromatography, preferably HPLC, will produce two successive peaks containing at least 80% of the aluminum present in the composition, wherein the ratio of the latter of said peaks, which is referred to as peak 4, to the former of said peaks, which is referred to as peak 3, is at least 1.0 with respect to height and at least 0.70 with respect to area.
It is also known that an antiperspirant salt may be conveniently formulated in aerosol form by suspending from 1 to 20% of powdered aluminum chlorhydrate in 1 to 25% of a carrier liquid along with 0.1 to 5% of a suspending agent and 50 to 95% of a propellant. See, for example, EP 274,252, GB 1,467,676 and U.S. Pat. No. 4,359,456. Typical carrier vehicles include cyclomethicone (volatile cyclic silicone) and isopropyl myristate, typical propellants include hydrocarbons and halogenated hydrocarbons, and typical suspending agents include hydrophobic clays, such as Bentone 38, and hydrophilic colloidal silicas such as Aerosil 200 and Cab-O-Sil M-5. Such aerosol formulations also often contain small amounts of a lower alkanol, such as ethanol, or some other polar agent, such as propylene carbonate, to interact with the clay suspending agent to improve the suspending properties.
When halogenated hydrocarbon propellants were replaced by hydrocarbon propellants, it became more difficult to formulate high quality aerosol antiperspirants. The need for a good suspending agent became much more critical in view of the much lower density of the hydrocarbon propellant versus the halogenated hydrocarbon propellant and not all of the previously utilized suspending agents were suitable for use in such aerosol formulations. For example, hydrophilic silica caused excessive viscosity build-up in processing concentrates containing cyclomethicone. Therefore, in such formulations the suspension system of choice was a quaternium hectorite hydrophobic clay (e.g., Bentone 38) in conjunction with a small amount of a polar additive (e.g., ethanol).
It has now been discovered that certain materials commonly used in traditional aerosol antiperspirant formulations have an adverse effect on antiperspirant efficacy, and particularly on the stability of high efficacy antiperspirant salts formulated as an aerosol composition. It has been further discovered that the efficacy of an aerosol antiperspirant formulation can be significantly improved and maintained at that level for a long period of time by removing those agents which have an adverse impact on efficacy.
One of the materials which-has an adverse effect on efficacy includes oil soluble emollient esters, that is high molecular weight esters commonly used as emollients. These esters particularly include the fatty acid esters, especially isopropyl myristate. Another one of the materials which has an adverse effect on efficacy includes polar materials such as lower alkanols, especially ethanol. While the presence of polar materials has no effect on conventional aluminum chlorhydrate salts, it has been found that when even small quantities as low as 1% are present in a composition containing a high efficacy aluminum chlorhydrate salt, the salt tends to revert from the high efficacy aluminum species toward the conventional form. This conversion is readily seen in HPLC chromatograms of the salt, where the peak 4 to peak 3 area ratio diminishes with time.
Since polar materials such as ethanol are often used in conjunction with conventional hydrophobic clay suspending agents, such as Bentone 38, to improve their suspension characteristics, the elimination of such polar agents in order to maintain efficacy requires that a different suspension system must be found to adequately formulate a high efficacy aerosol antiperspirant composition.
It is an object of the present invention to develop an aerosol antiperspirant composition with high antiperspirant efficacy. It is also an object to develop a high efficacy aerosol antiperspirant composition whose efficacy does not deteriorate with time. It is a further object to develop a high efficacy aerosol antiperspirant composition with a suspension system that provides advantageous suspension properties and good processing characteristics. It is also a further object to develop a high efficacy aerosol antiperspirant composition with all of the aforementioned characteristics and, in addition, with a low level of hydrocarbon propellant that meets California Air Resources Board environmental standards.